Why do grown-ups get periods?

Some grown-ups bleed because no baby is growing. Their body lets extra blood out. It comes from low in the belly. A pad can catch it.

Some grown-ups have a place inside where a baby could grow. Each month, the body makes a soft, bloody layer there. It is like putting a soft blanket in a crib. If no baby starts growing, the layer is not needed. So it comes out as blood. That is a period.

People with a uterus can have periods. The uterus is the place where a baby can grow. Each month, body messengers called hormones help make a soft lining inside it. If pregnancy does not happen, the lining is not needed, so it leaves the body through the vagina with some blood. Fun fact: humans are unusual, but not alone; some bats, primates, and tiny spiny mice have periods too.